The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 199 19 051.8, filed on Apr. 27, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a press section of a machine and process for producing a fiber web, in particular a paper, cardboard, or tissue web, having at least two press nips lying in succession in the web travel direction and each formed by two press rolls, with at least one separate, continuously revolving press belt being conducted around each press roll and, before and/or after at least one press nip, the fiber web running jointly with two press belts on opposite sides along a straight path in a guide region.
2. Discussion of Background Information
Such arrangements are generally known and are described, for example, in DE-OS 197 08 967. In these arrangements, turbulent air flows, in particular at high speeds, can cause the press felts to flutter, having an adverse effect on the quality of the paper as well as on the life of the press felts. Furthermore, the cross currents of air that likewise occur result in damage to the edge of the fiber web.
It is therefore the object of the invention to create a press section, while avoiding these disadvantages.
The object was achieved according to the invention in that, at the end of each guide region on the opposite side of the press nip, the press belts run separately from one another over guide elements such that the press belt angle between the press belts is greater than approximately 15xc2x0.
The bilateral guidance of the fiber web in the guide region is secure and stable even at high speeds and prevents damage to the fiber web. The relatively large press belt angle is necessary in this arrangement in order to reduce air turbulences and air flows oriented transverse to the fiber web in the entrance or exit twist of the press belts.
In order to guarantee a secure guidance of the fiber web even outside a guide region, the fiber web should be in constant contact with one of the press belts. It is advantageous in this situation for all the press belts to be formed as press felts or press screens to absorb the pressed water. It is also possible, in particular when the fiber web has a high dry content, to embody one of the two press belts of a press nip as a smooth press belt with little or no water-absorbing capacity.
A guide region of a certain length, which should preferably be greater than approximately 0.5 m, is a prerequisite for a particularly calm running of the press belts.
Since rotatable guide rolls are usually used as the guide elements of the press belts, the radius of these guide rolls influences the degree of air flow. In order to bring the press belts together or apart rapidly, the radius of the guide rolls should therefore be as small as possible, preferably less than approximately 0.8 m.
For adapting to changing operating conditions or different types of fiber webs, or for introducing the fiber web into the press section, it is advantageous for at least one guide element to be mounted in a movable fashion, so that the press belt angle can be changed by the position of a guide element. In order to be able to keep the tension of the press belt concerned relatively stable, this guide element should be movable perpendicular to the angle bisector of the looping angle of the respective press belt.
Such a secure guidance is provided if a guide region is present before and after each press nip.
However, it is also possible for the two press belts of a press nip to run separately before and/or after the press nip, with the press belt angle between the press belts being greater than 15xc2x0. This enables relatively compact arrangements. To reduce the air flows, however, all the press belt angles between the press belts should be greater than approximately 15xc2x0 and preferably greater than approximately 30xc2x0.
When the press belts run toward one another, the press belt not in contact with the fiber web should have air devices to remove the air boundary layer on the side facing the fiber web, which devices are preferably formed as a doctor, a compressed air nozzle, or a suction roll.
The present invention is directed to a press section of a machine for producing a fiber web. The press section includes at least two press nips arranged in succession in a web travel direction. Each of the at least two press nips is formed by two press rolls. At least one continuously revolving press belt is guided around each press roll. At least one of before and after at least one of the at least two press nips, a guide region is formed in which two of the press belts are arranged to run jointly along a straight path, and the fiber web is adapted to run between the two press belts along the straight path. Guide elements are arranged at an end of each guide region. At an end of each guide region, the press belts are guided over the guide elements to run separately from one another, and a press belt angle between the press belts at the guide elements is greater than approximately 15xc2x0.
According to a feature of the instant invention, the fiber web can include one of a paper, cardboard, or tissue web.
In accordance with another feature of the invention, the fiber web can be supported in a region of the press section by at least one press belt.
According to still another feature of the present invention, all the press belts can include press felts.
Further, the guide elements can include rotatable guide rolls having a radius smaller than approximately 0.8 m.
Moreover, at least one of the guide elements can be positionally movably mounted. In this manner, moving a position of the at least one guide element adjusts the press belt angle. The at least one guide element is movable substantially perpendicular to an angle bisector of a looping angle of a respective press belt around the at least one guide element.
In accordance with an aspect of the invention, guide regions can be arranged before and after each of the at least two press nips.
According to another aspect of the invention, the two press belts of at least one of the at least two press nips can be arranged to run separately at least one of before and after the at least one press nip, and a press belt angle between the two press belts of the at least one press nip can be greater than approximately 15xc2x0.
Further, all press belt angles between the press belts may be greater than 15xc2x0. Moreover, at least some of the press belt angles may be greater than approximately 30xc2x0.
The press section can also include air devices. The air devices may be arranged to remove an air boundary layer from a side of one of the press belts adapted to face the fiber web before the side makes contact with the fiber web. The air devices can include at least one of a doctor, a compressed air nozzle, and a suction roll.
In accordance with a further aspect of the invention, all guide regions can be longer than approximately 0.5 m.
According to still another aspect of the invention, the at least two press nips are extended in the web travel direction.
The instant invention is directed to a press section of a machine for manufacturing a fiber web. The press section includes a first press having a first and second press roll arranged to form a first nip, and a second press having a third and fourth press roll arranged to form a second nip. The first and second presses are successively arranged in a web travel direction. At least four press belts are provided. A first press belt is guided around the first press roll, a second press belt is guided around a second press roll, a third press belt is guided around the third press roll, and a fourth press belt is guided around the fourth press roll. A web guide region is arranged at least one of before and after at least one of the first and second nips. The web guide region includes a substantially straight path along which two of the at least four press belts are arranged to run jointly. At an end of the web guide region, the two press belt are arranged to separate at a belt angle greater than approximately 15xc2x0.
In accordance with a feature of the invention, at least one guide element may be positioned at an end of the web guide region, such that the two press belts separate at the at least one guide element. Further, at least one of the at least one guide element is a positionally movable guide element. Moving a position of the movable guide element adjusts the press belt angle. Still further, one of the two press belts can wrap around the movable element at a predetermined looping angle, and the movable element may be movable substantially perpendicularly to an angle bisector of the looping angle.
According to another feature of the invention, a web guide region can be arranged both before and after at least one of the first and second nips. Further, the web guide region may be arranged both before and after the first and second presses.
The first and second presses may be arranged to form first and second extended nips which are elongated in the web travel direction. At least one of the first and second press roll can be a shoe press roll, and at least one of the third and fourth press roll can be a shoe press roll.
According to a further feature of the present invention, the two press belts of at least one of the first and second press may be arranged to run separately at least one of entering and exiting a respective one of the at least one first and second nip, and a press belt angle between the two press belts at least one of entering and exiting the at least one first and second nip may be greater than approximately 15xc2x0.
In accordance with still another feature of the invention, a first separation angle formed by the separation of the first and second press belts can be greater than approximately 15xc2x0, and a second separation angle formed by the separation of the third and fourth press belts can be greater than approximately 15xc2x0. At least one of the first and second separation angle can be greater than approximately 30xc2x0. Further, the first and the second separation angles may be greater than approximately 30xc2x0.
The present invention is directed to a process of pressing a fiber web in a press section that includes at least two press nips, each of the at least two press nips being formed by two press rolls, at least one continuously revolving press belt being guided around each press roll, at least one guide region being formed at least one of before and after at least one of the two press nips, and guide elements arranged at an end of each guide region. The process includes successively pressing the fiber web in the at least two press nips, and jointly guiding the fiber web between two of the press belts in the at least one guide region. The at least one guide region includes a substantially straight path. The process also includes separating the two press belts at the guide element at the end of the at least one guide region at a separation angle of at least 15xc2x0.
According to a feature of the present invention, the process further includes guiding the fiber through one of the at least one guide regions which exits the second press nip in a web travel direction. The process can also include guiding the fiber web through another of the at least one guide regions which enters the second press nip, and guiding the fiber through another of the at least one guide regions which exits the first press nip in the web travel direction. The process can also include separating the fiber web from one of the press belts when exiting the first press nip in the web travel direction. A separation angle of the press belt exiting the first nip can be greater than 15xc2x0. Moreover, the process can include separating the press belts upon exiting the first press nip in the web travel direction.
In accordance with yet another feature of the instant invention, the at least one guide region can be located after the first press nip in the web travel direction, and the process can also include adjusting the separation angle at the end of the at least one guide region by moving the guide element. The guide element may be movable in a direction substantially perpendicular to an angle bisector of a looping angle of one of the press belts around the guide element.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.